The invention relates to iridium and the Zr- and Hf-free alloys thereof, as well as to rhodium and the Zr- and Hf-free alloys thereof, having high creep rupture strength at high temperatures.
Iridium, one of the metals of the platinum group, is used for example in crucibles for growing single crystals of high-melting oxidic melts, e.g. of Nd:YAG laser crystals, or in components for the glass industry. For these applications, not only the corrosion resistance with respect to oxidic melts, but also high creep resistance and creep rupture strength of the iridium at high temperatures are of crucial importance.
A method for increasing the creep resistance and creep rupture strength of iridium alloys is described in German published patent application DE 10 2005 032 591 A1. It involves doping with molybdenum, hafnium, and possibly rhenium, whereby the sum of molybdenum and hafnium is between 0.002 and 1.2 percent by weight. This allowed the time to rupture exposed to a load of 16.9 MPa to be increased more than two-fold as compared to undoped iridium.
International patent application Publication No. WO 2004/007782 A1 describes tungsten- and/or zirconium-containing iridium alloys for high temperature applications, which contain 0.01 to 0.5 percent by weight of further elements, such as molybdenum and hafnium and possibly 0.01 to 10 percent by weight ruthenium.
Japanese patent application publication no. JP 56-81646 A describes platinum-based jewellery alloys that contain calcium boride or boron to increase their strength, mainly their hardness, after a high temperature treatment, such as soldering.